Device for continuously preheating a mixture of burnable gas, more particularly natural gas and oxygen

ABSTRACT

The invention relates to a device for continuously preheating a mixture of burnable gas, particularly natural gas and oxygen, prior to the catalytic combustion thereof, wherein the combustion heat thereof can be used to heat fed-out natural gas, before or after the expansion thereof and supply to consumers, in order to compensate for the Joule-Thomson effect. The device is designed as a jet pump having a propelling nozzle and a diffuser aligned therewith. The propelling nozzle is the inlet for the mixture into a mixing chamber disposed in the pump housing, a suction line for the natural gas heated by means of catalytic combustion being connected to the chamber. The diffuser is part of an outlet of the mixing chamber of the jet pump. The propelling nozzle and the diffuser are disposed such that they can be moved relative to one another in the pump housing. An adjusting mechanism is provided for adjusting the distance between the propelling nozzle and the diffuser as a function of the temperature of the gas mixture flowing out of the mixing chamber through the outlet.

The invention relates to a device for continuously preheating a mixture of burnable gas, more particularly natural gas and oxygen prior to the catalytic combustion thereof, wherein its combustion heat can be used to heat fed-out natural gas before or after the expansion thereof and supply to consumers, in order to compensate for the Joule-Thomson effect.

A device of the above type is known from EP 0 920 578.

In the method implemented with the known device, through the catalytic conversion of oxygen with natural gas in the strongly substoichiometric mixing range on the catalyst, directly in the gas flow, temperatures of up to 400° C. are attained.

In principle, self-ignition can never be entirely ruled out when directly adding oxygen to burnable gases. However, by selecting the pressure, temperature and concentration parameters the risk of undesirable self-ignition can be reduced.

Catalytic combustion requires a catalyst activation temperature of around 180° Celsius to 250° Celsius. The preheating of natural gas-oxygen mixtures to this catalyst activation temperature cannot be technically implemented before expansion in relation to self-ignition at the prevailing high pressures. Safe feeding out of the natural gas is not possible.

The self-ignition of natural gas-oxygen mixtures is pressure and temperature dependent, so that an increase in oxygen concentration already leads to combustion in the gas flow and thereby to an increase in pressure and temperature even without catalyst. This is a disadvantage as the combustion process cannot then be controlled.

Before entering the catalytic reactor the fed-out natural gas-oxygen mixture is at a temperature of around 5° Celsius to 30° Celsius so that it is quite cold and far below the required activation temperature range. The required combustion process therefore becomes imbalanced after only a short time. Below the activation temperature the reactor is “cold blown” and the oxygen remains in the natural gas without having been converted.

The aim of the invention is to provide a device which allows safe preheating, and thereby a stable process of catalytic conversion of oxygen and natural gas.

This objective is achieved by the features of claim 1. Further developments and advantageous embodiments are set out in claims 1 to 5.

According to the invention the device is designed as a jet pump, the function of which is to supply to the fed-out cold natural gas flow, which is at temperatures of 5° Celsius to 30° Celsius, warm natural gas from the reactor, exhibiting temperatures of 250° Celsius to 400° Celsius through generating an underpressure in the mixing chamber of the jet pump. This inlet function is particularly preferably temperature-regulated and means that the catalyser is not blow out of the active temperature of at least 180° Celsius for the following reaction between natural gas and oxygen.

This is guaranteed in that the propelling nozzle and the diffuser are arranged so as to be movable relative to each other in the pump housing, more particularly in its mixing chamber, whereby an adjusting mechanism ensures temperature-dependent adjustment of the distance between the propelling nozzle and diffuser for the gas mixture to flow out of the mixing chamber.

As the adjusting mechanism has at least one operating cylinder supported on the housing with a piston rod arranged on the diffuser guided adjustably along a guide, the distance between the propelling nozzle and diffuser is changed.

Connected to the mixing chamber of the jet pump is a suction line, which draws natural gas already heated by the catalytic combustion process into the mixing chamber. The heated natural gas is at the required temperature of 250° Celsius to 400° Celsius and in the mixing chamber is swirled and mixed with the cold natural gas-oxygen mixture, whereby the mixture is heated to a predetermined desired temperature and finally flows out of the mixing chamber through the outlet as a preheated gas mixture. This preheated gas mixture then again undergoes catalytic combustion, from which, as has already been described, a warm partial gas follow is continuously diverted via the suction line.

In accordance with an advantageous further development of the invention, the diffuser is a hollow cylindrical component, which is disposed in a longitudinally adjustable manner on the outlet of a pipe emerging from the mixing chamber and housing for emission of the now preheated gas mixture.

The longitudinal adjustability produces the adjustment path of the diffuser vis-a-vis the propelling nozzle, which is inserted in a stationary, i.e. fixed, manner into the housing. Via a control valve, which as a function of the temperature of the gas mixture flowing through the outlet determined by measuring sensors, acts on three operating cylinders arranged around the circumference of the diffuser, the diffuser can be moved in a temperature-controlled manner in such a way that it can be moved towards or away from the propelling nozzle. The temperature of the gas mixture leaving the mixing chamber can thereby be continuously regulated.

By means of return springs built into the cylinder chambers of the operating cylinder, the pistons of the operating cylinder are always pressed back into the end position. When the control valve is fully opened to operate the piston, the diffuser moves towards the propelling nozzle so that only relatively cold natural gas can reach the outlet of the device and the catalyst in order to deactivate and/or “cold blow” the latter.

The pressure medium used to control the diffuser is natural gas which is diverted from the main flow of natural gas to the heating reactor, namely before a corresponding control valve in the area of the inlet into the rector in which the catalytic combustion of the natural gas in order to heat it takes place. At this diversion point there is always sufficiently high pressure present to operate the pistons under the control of the control and regulating device.

The gas which is used to control the pistons can through appropriate selection of clearances between the piston and cylinder wall also flow off into the mixing chamber of the device designed as a jet pump.

When the control valve is closed, such “leakage losses” result in a pressure equalization and through the built-in return spring in the cylinders the pistons are pressed back into their original position.

The device advantageously allows preheating of the gas mixture before it enters the reactor and also controlled “cold blowing” of the catalytic reactor in which heating of the entire fed-out natural gas takes place, whereby ultimately through mixing in the gas mixture heated to 250° Celsius to 400° C. Celsius with the heat released in the reactor to the fed-out natural gas flow, the latter is continuously heated in order to compensate for the Joule-Thomson effect that occurs during expansion.

The device also brings about an advantageous dilution of the oxygen-natural gas mixture in an area which is with certainty below the self-ignition level, which makes carrying out the catalytic combustion considerably safer.

Through the continuous adjustability of the distance between the propelling, nozzle and the diffuser, controlled self-maintenance of the catalytic reaction with subsequent combustion of the natural gas-oxygen gas mixture is possible.

Additional drives, fans or suchlike are not necessary in the device in accordance with the invention as it is controlled by the available fed-out natural gas, i.e. through its own medium.

An example of embodiment of the invention, which sets out further inventive features, is shown in the drawing.

FIG. 1 shows a side view of the device in cross-section, and

FIG. 2 shows the incorporation of the device into a process of utilising the combustion heat from the catalytic combustion of a mixture of natural gas and oxygen in the form of a flow diagram.

FIG. 1 shows a side view of the device for continuously preheating a mixture of burnable gas, more particularly natural gas and oxygen, in cross-section.

The mixture of natural gas and oxygen is provided in a mixing container 18, which is not shown here in more detail, and flows at the corresponding high feed-out pressure into the device via inlet connection 1. The device is designed as a jet pump 2 which has a propelling nozzle 3 via which the supplied mixture of natural gas and oxygen is forced into a mixing chamber 5 located in the pump housing 4.

Connected to the mixing chamber is a suction line 6 via which the partial flow of the natural gas already heated in a reactor 15 can be drawn into the mixing chamber 5 when the propelling nozzle forces it into the diffuser 7 aligned opposite it.

The diffuser is hollow cylindrical component, which is disposed in a longitudinally adjustable manner on the outlet 8 of a pipe 9 emerging from the mixing chamber 5 and housing 4 for the outlet 10 of the gas mixture preheated in the mixing chamber 5.

The jet pump 2 has an adjusting mechanism for adjusting the distance between the propelling nozzle 3 and diffuser 7 as a function of the temperature of the gas mixture flowing out through the outlet of the mixing chamber 5. The adjusting mechanism comprises several operating cylinders arranged on the housing 4 of which only the visible operating cylinder 11 is shown here. The piston rod 12 of the operating cylinder 11 is attached to diffuser 7, which is adjustably moved along its guide on pipe 9, at pivot point 12.

Each operating cylinder 11 has a connection for the controlled supply of pressure medium by means of a control and regulating device, which is not shown in more detail here.

FIG. 2 shows a flow diagram and illustrates the arrangement of the device in accordance with FIG. 1 within a device for heating fed-out natural gas before or after its expansion and introduction into a supply network. The fed-out natural gas flows via the main line 14 via a control valve into the ring chamber of the reactor 15 in which it is heated before it flows into a supply line 16. In the reactor 15 combustion of a gas mixture of natural gas and a natural gas-oxygen mixture takes place.

The natural gas for the gas mixture for combustion is diverted from the main flow 14 via the partial flow line 17 and is enriched in the mixing container 18 with the oxygen necessary for attaining the required mixing ratio (e.g. 3 MOl %). The mixture of natural gas and oxygen enters the mixing chamber 5 via the propelling nozzle 3. In connection with the diffuser 7 an underpressure is generated in the mixing chamber 5 which draws warm natural gas from the reactor 15 via the suction line 6. This is mixed with the cold natural gas flow blown in via the propelling nozzle 3, and the thus heated/preheated mixture flow out of the mixing chamber 5 via the outlet 10 into the reactor 15. The catalytic combustion which takes place there releases heat with which the fed-out natural gas supplied via the main line 14 is heated through continuous mixing before, via line 16, it reaches a station where it is expanded, for example to a comparatively low pressure present in a supply line.

The adjusting mechanism for the diffuser 7 is indicated schematically here. The longitudinal displacement is indicated symbolically with the double arrow 19.

The drawn-in operating cylinders of the adjustment mechanism 11, 11′ are supported on the pump housing 4. The piston rods 20 of the operating cylinders are, as shown here, pivotably connected to the diffuser 7 and 20 and 20′ respectively.

21 and 21′ denote return springs.

For the supply of pressure medium to the operating cylinders 11, 11′ a branch 22 is provided which is connected at diversion point 23 to the main line 14 for fed-out natural gas.

A control and regulating device comprises a control valve 24 and a temperature sensor 25 which measures the temperature of the preheated gas mixture flowing into the reactor 15 via outlet 10 and acts on the control valve 24 in such a way that it opens further or closes, whereby more or less pressure medium is supplied to the operating cylinders via the branch line 22. This supply of pressure medium via the branch line 22 a temperature-dependent longitudinal displacement of the diffuser 7 on the pipe of outlet 10.

The suction effect of the jet pump can be increased further and/or influence by an additional conveying means 26. 

1. A device for continuously preheating a mixture of burnable gas, more particularly natural gas and oxygen prior to its catalytic combustion, wherein the combustion heat thereof can be used to heat fed-out natural gas, before or after its expansion and supply to consumers, in order to compensate for the Joule-Thomson effect, wherein it is designed as a jet pump with a propelling nozzle (3) and a diffuser (7) aligned therewith, wherein the propelling nozzle (3) is the inlet for the mixture into a mixing chamber (5) disposed in the pump housing (4), wherein a suction line (6) for the natural gas heated by means of the catalytic combustion is connected to the mixing chamber (5), wherein the diffuser (7) is part of an outlet (8) of the mixing chamber (5) of the jet pump, wherein the propelling nozzle (3) and the diffuser (7) are arranged in the pump housing (4) such that they can move relative to each other and wherein an adjusting mechanism is provided for adjusting the distance between the propelling nozzle (3) and the diffuser (7) as a function of the temperature of the gas mixture flowing out the mixing chamber (5) through the outlet.
 2. The device in accordance with claim 1, wherein the adjusting mechanism comprises at least one operating cylinder (11, 11′) supported on the pump housing (4), the piston rod of which is pivoted on the diffuser (7) which is adjustably displaced along a guide.
 3. The device in accordance with claim 2, wherein each operating cylinder (11, 11′) has a return spring (21, 21′).
 4. The device in accordance with claim 1, wherein the diffuser (7) is a hollow cylindrical component which is disposed on the outlet (8) designed as guide of a pipe (10) emerging from the mixing chamber (5) and pump housing (4) for the outlet of the preheated gas mixture.
 5. The device in accordance with claim 1, wherein each operating cylinder (11, 11′) has a connection for the supply of pressure medium controlled by a control and regulating device.
 6. The device in accordance with claim 5, wherein for the supply of pressure medium a branch line (22) is provided which branches off from a main line (14) for fed-out natural gas. 